Ventilation device for transmissions with lubricant comprising water

ABSTRACT

A ventilation device for transmissions with lubricant comprising water, the device being disposed above the transmission ( 1 ) and being connected thereto by way of a line ( 10 ) and comprising a pressure equalization opening ( 13 ) that leads to the surrounding environment, is to operate without loss of evaporating water to the environment. To this end, the device comprises at least one container ( 17 ) designed as a condenser for evaporated water rising through the line ( 10 ), the container being provided with a cooling element for dissipating heat ( 15 ), the condensate passing from said container ( 17 ) back to the transmission ( 1 ). In one variant, two containers containing a fluid are described which communicate with one another by way of a U-shaped channel.

BACKGROUND OF THE INVENTION

The invention relates to a ventilation device for transmissions with alubricant containing water, wherein the ventilation device is connectedto the transmission housing via a line and has a pressure equalizationopening leading to the environment.

In oil-lubricated transmissions there is a ventilation opening, whichallows pressure equalization with the environment when the temperaturein the transmission rises or falls due to operating conditions and whichis usually equipped as a device with installations for retaining oilmist and for keeping away dirt from the environment.

WO 2007/098523 A1 discloses a lubricant containing water, which inaddition to a high proportion of water contains an agent lowering thefreezing point, such as glycol, and further additives and/or suspendedmatters. Further details as well as the advantages to be obtained withsuch a lubricant can be gathered from the above-mentioned publication.

DE 22 20 565 discloses a recirculating cooling system for oil-lubricatedreduction transmissions. A fan recirculates air containing oil vaporsfrom inside the transmission through a heat exchanger back into thetransmission. The condensed oil is returned separately. There is nopressure equalization with the environment.

Water has a very low vapor pressure in comparison to lubricating oil, sothat it evaporates easily. This leads to the fact that not only theamount of lubricant in the transmission becomes less and less, whichsoon results in the destruction of the transmission, but also thecomposition of the lubricant changes because the proportion of waterbecomes smaller and smaller.

Thus it is the object underlying the invention to remedy thisdisadvantage and to counteract the loss of water to the environment.

SUMMARY OF THE INVENTION

According to the invention, this is achieved by the fact that theventilation device comprises at least one container formed as acondenser to which evaporated water passes through the line, saidcontainer being provided for this purpose with means for dissipatingheat, wherein the condensate passes from said container back to thetransmission.

When the transmission is heated up due to operating conditions, the airwhich is present in the lubricant-free space expands and there isincreased evaporation, so that a mixture of air and water vapor flowsthrough the line into the evaporating device. In the evaporating devicethe water vapor is condensed and the air is allowed to escape into theenvironment. Thus a separation of air and water vapor and a condensationof the water vapor occur simultaneously with the pressure equalization.

Heat dissipation is required for the condensation, which heatdissipation is achieved in various ways. Either by a group of pipesmounted inside the at least one container and flown through by asuitable cooling agent or by cooling ribs arranged at the outside of thecontainer, or a combination of both. If the transmission is part of amotor vehicle, the cooling ribs should be exposed to the air stream, ifpossible. This is easily possible due to the fact that the device doesnot need to be mounted at the transmission itself, but is connectedthereto by a line. If the line continuously rises and its cross sectionis sufficiently dimensioned, it can at the same time serve as a returnline for condensed water. In this way, only a single tube is requiredbetween the transmission and the device.

However, the device can also be arranged at the same height as or lowerthan the transmission. In these cases the line, at least in thecontainer, leads downwards and ends below the level of the condensate.In this way, the condensate can be drawn back in the case of a pressuredrop in the transmission.

In an advantageous further development of the invention, the deviceconsists of two containers arranged essentially at the same geodeticheight and containing a liquid, wherein the deepest points of the twocontainers communicate with one another via a U-shaped duct and whereinthe line opens into one of the containers and the other container hasthe pressure equalizer opening at its top. The two containers areinterconnected in the manner of a siphon. When the pressure changes inthe transmission, the liquid is displaced in the siphon, wherein thelevels of liquid in the two containers move apart from one another.Water vapor condenses in the liquid, wherein a part thereof flows backinto the transmission when the level of liquid has increasedsufficiently or the pressure in the transmission has dropped.

Previously to the initial operation, the siphon and the two containersare filled with such a large amount of liquid that their levels in thisinitial state reaches up to the orifice of the line. Due to this factreturning the condensate into the transmission becomes more even.

The liquid in the siphon and in the two containers can be water, anagent lowering the freezing point, for example, glycol or a mixture ofboth. Depending on the conditions and requirements, the one or the otheris to be preferred. If no temperatures below the freezing point are tobe expected, water is preferable because in this way the composition ofthe lubricating liquid in the transmission remains unchanged. Otherwisethe agent lowering the freezing point is more advantageous.

In a further development of the invention, the space filled with liquidcontains a porous material of high thermal conductivity. This improvesheat transfer and condensation and prevents fluctuating of the levels ofliquid in the two containers. As the porous material, in particularstainless steel wool has proved its worthiness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: schematic representation of the device according to theinvention in a first embodiment;

FIG. 2: schematic representation of the device according to theinvention in a second embodiment, in its initial position;

FIG. 3 like FIG. 2, when the transmission is heated up;

FIG. 4 like FIG. 2, when the transmission is cooled down;

FIG. 5 schematic representation of the device according to the inventionin a third embodiment.

DETAILED DESCRIPTION

In FIG. 1, a transmission is designated summarily with reference numeral1 and a ventilation device according to the invention with referencenumeral 11. As a simplifying example, the transmission 1 herein containsa driving shaft 6 having a gear 5 and a driven shaft 8 having a gear V.Details which are common for transmissions, such as bearing and housingpartition, are not elaborated on. In practice, it can be anytransmission, such as the shift gearbox or the rear-axle transmissionwith differential of a motor vehicle.

The lower part of the transmission contains a lubricating liquid 2having a level 4. The gear 7 immerges into the lubricating liquid 2. Theupper region of the transmission 1 has an opening 9. Otherwise thetransmission 1 is closed and thus has no flow connection with theenvironment. The lubricating liquid contains a considerable amount ofwater and is described in more detail in WO 2007/098523 A1. A line 10leads steadily upwards from the opening 9 up to the ventilation device11 according to the invention. In this case, the ventilation device 11comprises a container 17, inside of which there is a cooling pipe coil15. It is flown through by a preferably liquid cooling agent.Alternatively or additionally the container 17 can be provided withcooling ribs 16. The container 17 has an opening 13 at its highestpoint, which, as a conventional ventilation opening, protects againstthe intrusion of dirt with a cap 14.

By way of this simplest embodiment of FIG. 1, the basis of the functioncan be recognized. The water evaporating due to friction and heating inthe transmission 1 (and, if applicable, further liquids present in thelubricant) rises via the line 10 into the ventilation device 11. Thereit condenses due to cooling, and the condensate flows back again intothe transmission 1. Since the ventilation device 11 is a separate unit,it can also be arranged at some distance from the transmission, such asat a place where it is exposed to the air stream. In this case thecooling ribs are useful; otherwise dissipation of the condensation heatis primarily effected by the cooling pipe coil 15. Due to the opening 13there is no change in pressure in the transmission or in the container17.

In the embodiment of FIG. 2 the ventilation device is formed by twocontainers, a first container 21 and a second container 22, bothessentially at the same geodetic height, thus side by side. The line 10rising from the transmission opens into the first container 21 at acertain height (orifice 23). At its highest point the second container22 has a conventional ventilation opening making the connection with theenvironment. The lowermost points 25, 26 of the two containers 21, 22are interconnected via a U-shaped pipe 27, so that they form vesselscommunicating for a liquid.

The U-shaped pipe 27 and the lowermost regions of the two containers 21,22 are filled with a liquid corresponding to the levels of liquid 30,31. The spaces 28 and 29, respectively, on top of it contain air andwater vapor. In the initial position shown in FIG. 2 (previously to thefirst operation of the transmission), both levels 30, 31 are equallyhigh. Herein the level 30 is somewhat below the orifice 23 of the line10. The liquid is one of the components of the lubricating liquid or thelubricant itself or a mixture of their components.

In addition to the filling of liquid, the U-shaped pipe 27 and the lowerregions of the two containers 21, 22 still contain another filling 32made of a porous material, which takes up and conducts heat well. Thoughthis filling 32 is to allow the flow of the liquid between the twocontainers 21, 22, it dampens it. The main function of the filling 32 isto take up and dissipate heat, see further description of functionhereinafter. Stainless steel wool has proven to be especially efficientfor this purpose, not least due to its good thermal conductivity. TheU-shaped pipe 27 can be additionally provided with cooling ribs 33.

In order to explain the function, at first the transition from theinitial state of FIG. 2 to the state of FIG. 3 will be described: Duringoperation the transmission heats up and with it the lubricant, whereinthe water contained therein begins to evaporate and the air/vapormixture expands in the space above the lubricant. This causes themixture to rise through the duct 10 into the space 28, in which themixture at first displaces the liquid present there—causing the level 30to decrease to 30′—and subsequently bubbles through the liquid in theU-shaped pipe 27. Herein the water vapor condenses—especially fast dueto the fact that it touches the filling 32—, and the air reaches thesecond container 22. The air rises therein and exits—just as the airdisplaced by the risen level 31′—through the ventilation opening 34 intothe environment. If the liquid in the U-shaped pipe 27 and in the lowerregions of the two containers 21, 22 contains a substance lowering thefreezing point (glycol or another superior-grade alcohol), thissubstance absorbs the water vapor, wherein its volume is increased, andmixes with the condensate. Thus the condensing effect of thisarrangement is a multiple one.

In order to explain the function, furthermore the transition from thestate of FIG. 3 to the state of FIG. 4 will be described: when thetransmission is stopped, it cools down relatively quickly, and with itthe air/vapor mixture present in the space 28 of the first container 21.Due to this fact a vacuum develops in the space 28, causing the level30′ in the first container 21 to rise to the level 30″ andcorrespondingly the level 31′ to decrease to the level 31″. This is notimpeded since air is able to flow in through the ventilation opening.However, the flow in the duct 27 is retarded by its filling 32 of steelwool. The rising level 30″ in the first container 21 finally reaches theopening 23, in which the downwards leading line 10 opens into thecontainer 21. Due to the fact that the volume of the filling of liquidhas increased by absorbing water and mixing with water, the additionalamount flows back into the transmission 1 through the line 10. Thisensures that amount and mixing ratio of the total amount of liquid donot change.

The embodiment of FIG. 5 differs from the one of FIG. 1 in that the line110 in the container 117 is led downwards far enough for its open end123 to immerge into the condensed water 132. The end 123 lies below thelevel of liquid 130, so that, when the transmission is cooled down,condensate is drawn back into the transmission. Due to this fact thereis great freedom in arranging the container 117. It can be placed in thevehicle such that it is exposed to the air stream, even near the ground.

Within the framework of the invention, the described embodiments can bemodified in various ways; in particular, individual features thereof canbe combined with one another.

1. A ventilation device for transmissions with a lubricant containingwater, said ventilation device being connected to the transmission (1)via a line (10; 110) and having a pressure equalization opening (13;113) which leads to the environment, wherein the ventilation devicecomprises at least one container (17; 21, 22; 117) formed as a condenserfor evaporated water flowing thereto through the line (10; 110), saidcontainer (17; 21, 22; 117) being provided for this purpose with meansfor dissipating heat (15; 16; 32; 33; 115), wherein the condensatepasses from said container (17; 21, 22; 117) back into the transmission(1).
 2. The ventilation device according to claim 1, wherein the meansfor dissipating heat is a group of pipes (15) mounted inside the atleast one container (17) and flown through by a suitable cooling agent.3. The ventilation device according to claim 1, wherein the means fordissipating heat are cooling ribs (16) arranged at the outside of theone container (17; 21, 22).
 4. The ventilation device according to claim1, wherein the line (10) continuously rises, so that it also serves as aline for returning condensed water.
 5. The ventilation device accordingto claim 1, wherein the line (110) leading to the container (117)immerges into the container deeply enough for its opening (123) to bebelow the level of liquid (130) present in the container (117).
 6. Theventilation device according to claim 1, wherein it is formed by twocontainers (21, 22) containing a liquid, wherein the deepest points (25,26) of the two containers (21, 22) communicate with one another via aU-shaped duct (27), wherein the line (10) opens into the one container(21) and the other container (22) has the pressure equalizer opening(34).
 7. The ventilation device according to claim 6, wherein the level(30, 31) of the liquid in the initial state reaches up to the orifice(23) of the line (10).
 8. The ventilation device according to claim 6,wherein the liquid in the U-shaped duct (27) and between the levels (30,31) is water.
 9. The ventilation device according to claim 6, whereinthe liquid in the U-shaped duct (27) and between the levels (30, 31) inwhole or in part is an agent lowering the freezing point, for example,glycol.
 10. The ventilation device according to claim 6, wherein thespace filled with liquid is filled with a porous material (32) of highthermal conductivity.
 11. The ventilation device according to claim 9,wherein the porous material (32) is stainless steel wool.